Stabilising band for a roller assembly

ABSTRACT

The invention relates to a stabilising band for a roller assembly of the type used in the drilling industry. The roller assembly includes a roller pin mounted within a bore of a roller and the stabilising band is configured so as to fit tightly about the roller pin with a minimal running fit and within an annular groove formed in a wall of the bore of the roller.

FIELD OF THE INVENTION

The present invention relates to a stabilising band for a rollerassembly.

BACKGROUND OF THE INVENTION

During drilling operations, a drill bit is subject to wear and thus thedimension of the drill hole will vary over time. To ensure that thedimension of the drill hole is held true, rotary roller reamers arelocated in the drill string above the drill bit and are used to ream outthe drill hole to the required dimension. The inclusion of rotary rollerreamers in the drill string enables the drill bit to be used for alonger period without changeover and this prevents considerable costlydowntime.

A rotar roller reamer typically includes a number of roller assembliesmounted about its periphery. Each roller assembly will normally includea crushing roller mounted on a roller pin so as to rotate thereabout.

However, the working environment of a rotary roller reamer (and thusthese roller assemblies) is very harsh, and any parts that requirerelative rotation (such as between each crushing roller and its rollerpin) need to be adequately sealed to prevent the ingress of anycontaminants and to maintain any internal lubricants in an acceptablestate. Accordingly, a seal is typically provided at or adjacent toeither end of the roller. Such a seal may adopt numerous different formsbut may be a conventional o-ring seal. It is recognized that in somesituations, for example when the roller assembly is subject to highimpact compression, resulting movement of the roller pin may cause theintegrity of these seals to be lost.

The present invention aims to facilitate maintenance of the integrity ofthe seals.

SUMMARY OF THE INVENTION

According to the present invention there is provided a stabilising bandfor a roller assembly, the roller assembly having a roller pin mountedwithin a bore of a roller body, the stabilising band being configured soas to fit tightly about the roller pin with a minimal running fit andwithin an annular groove formed in a wall of the bore of the rollerbody.

Preferably, the roller pin is rotatably mounted within the bore of theroller body.

The stabilising band may be endless or may be broken (discontinuous) andwill preferably float within the groove, in that it may either berotatable with the roller pin or with the roller body.

Such a stabilising band is preferably made of a material that isreasonably hard and has a relatively low coefficient of friction. Thismaterial may be a fluoropolymer selected from the range ofpolytetrafluorethylenes (PTFE) marketed by DuPont under the TEFLON®trade mark. However, more preferably, such a material will bestrengthened by the addition of filler, such as with a glass, bronze ornickel filler. Ideally, the material will be a bronze filled PTFE.

In this form, the stabilising band tends to assist in maintaining therotation of the roller pin substantially stable about its longitudinalaxis and along its entire length. In this respect, in some situations,the seals between the roller pin and the roller will be somewhatsensitive to end-to-end bounce of the roller pin. Such bounce wouldnormally be expected to incur due to the reasonably severe impactcompression encountered by the roller assembly during operation. The useof a stabilising band of this type will thus assist with the smoothoperation of the roller assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away view of a rotary roller reamer incorporating astabilising band in accordance with an embodiment of the invention;

FIG. 1A is an enlarged view of the central portion (i.e. the pocket andthe roller assembly) of the rotary roller reamer shown in FIG. 1;

FIG. 2 is a partial assembly view of a roller assembly adjacent to areamer body having multiple pockets;

FIG. 3 is a central longitudinal cross sectional view of the rollerassembly shown in FIG. 2 mounted in a pocket of a rotary roller;

FIG. 3A is a part cross sectional view of one end of the roller assemblyalong a line offset from the centre line of the rotary roller reamer;

-   -   FIG. 4 is a longitudinal cross sectional view of the pocket of        the rotary roller reamer shown in FIG. 3;

FIGS. 5 to 8 are perspective views of the first retaining means;

FIGS. 9 to 11 are perspective views of the second retaining means;

FIG. 12 is a side view of the crushing roller;

FIG. 13 is a longitudinal cross sectional view of the crushing rollershown in FIG. 12;

FIG. 14 is an end view of the crushing roller shown in FIG. 12;

FIGS. 15 to 17 are views of the roller pin;

FIG. 18 is a cross sectional view showing connection of the firstretaining means to the connector screw which extends from the enlargedhead of the roller pin;

FIG. 19 is cross sectional view showing insertion of the retaining plugin the connector screw slot of the first retaining means;

FIG. 20 is a partial cross sectional view showing insertion of a rollercartridge (i.e. the assembled roller assembly) into a pocket of therotary reamer;

FIG. 21 is a perspective view of the stabilization band shown in FIG.1A;

FIG. 22 is a front view of the stabilization band shown in FIG. 21;

FIG. 23 is a side view of the stabilization band shown in FIG. 21; and

FIG. 24 is a cut-away view of another from of roller assemblyincorporating stabilising rings in accordance with an embodiment of theinvention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 1A illustrate a rotary roller reamer 10. The rotary rollerreamer 10 has a male end 12 and a female end 14. The rotary rollerreamer 10 is arranged to be attached to a drill string (not shown). Asshown in this embodiment, the male end 12 is located at the down holeend of the rotary roller reamer 10 and the female end 14 is located atthe up hole end of the rotary roller reamer 10. It will of course beappreciated that the configuration or nature of the respective ends ofthe rotary roller reamer 10 may vary.

The rotary roller reamer 10 includes a tubular reamer body 16 whichincludes three circumferentially spaced pockets 18. Located within eachpocket 18 is a roller assembly or roller cartridge 20. The pockets 18 asillustrated are equally spaced about the periphery of the reamer body 16and are located in a section 16 a of the body 16 that has a larger outerdiameter than the remainder of the body 16. Although three pockets 18are illustrated, it will be appreciated that arrangements with differentnumbers of pockets 18 and spacings are envisaged.

FIG. 2 better illustrates the pockets 18 formed in the reamer body 16.This figure also illustrates the cut away sections or mud ways 17 formedbetween adjacent pockets 18.

FIG. 2 illustrates the roller assembly 20 in a disassembled condition.The roller assembly 20 includes a roller pin 22, a crushing roller 24, afirst retaining means 26, a second retaining means 28, a retaining screw29, a first thrust ring 30, a second thrust ring 32, a pair of seals 34a, 34 b, a pressure equalisation means 36, a fastener 38, a pair of selflocking pins 38 a, a connector screw 70 and a retaining plug 72.

When the components of the roler assembly 20 are assembled together theyform a single cartridge which can be secured, using the fastener 38, inthe pocket 18 of the rotary roller 10. During use, the crushing roller24 is arranged to rotate about the roller pin 22 so that it can be usedto ream the sidewalls of the drill hole through which the rotary rollerreamer 10 is passed. The nature of each of the components of the rollerassembly 20 and the pockets 18 formed in the reamer body 16 will now bedescribed in more detail.

FIGS. 3, 3A and 4 best illustrate the configuration of each of thepockets 18 and the engagement of the roller assembly 20 within itsrespective pocket 18. Each pocket 18 includes a lower tapered. socket40, a primary cavity 42, a secondary cavity 44 and an upper taperedsocket 46. The lower tapered socket 40 is located at the down hole endof the rotary roller reamer 10, whilst the upper tapered socket 46 islocated at the up hole end of the rotary roller reamer 10. The lowertapered socket 40 is arranged to receive the second retaining means 28,whilst the upper tapered socket 46 is arranged to receive the firstretaining means 26. The primary cavity 42 is arranged to receive theroller pin 22 and the crushing roller 24 which is mounted thereon. Theprimary cavity 42 is sized and configured to provide operating clearancefor the crushing roller 24 during use of the rotary roller reamer 10.The secondary cavity 44 forms a seat for the head 22 a of the roller pin22.

The lower tapered socket 40 includes a semi-circular truncated conicalseat of less than or equal to 7° angle to a normal axis of the socket 18(i.e. the axis normal to the longitudinal axis of the rotary rollerreamer 10). As illustrated, this angle is approximately 3°. The lowertapered socket 40 is tapered so that the larger diameter of the socket40 forms part of the floor 18 a of the pocket 18. Tangential to theconical seat is an entrance guide way 40 a having sides matching thetaper of the conical seat.

Formed in the lower part of the lower tapered socket 40 and coincidentwith the floor 18 a of the pocket 18, is a semi-circular recess 40 b.This recess 40 b is a security recess which is arranged to receive acomplimentary shaped lug 28 k formed on the second retaining means 28.The function of the security recess 40 b and the lug 28 k will bediscussed in more detail subsequently.

Installed in a portion of the floor 18 a of the lower tapered socket 40so as to be positioned below the head 22 a of the roller pin 22 are fourcarbide inserts 18 b. The carbide inserts 18 b are provided to preventwear of the floor 18 a of the pocket 18 due to movement of the head 22 aduring use of the rotary roller reamer 10.

The primary cavity 42, as clearly illustrated in FIG. 4, is necked downas compared to the external diameter of the reamer body 16.Additionally, the floor 18 a of the primary cavity 42 steps downwardlyin a direction towards the centre line of the reamer body 16. Thus, theprimary cavity 42 has a depth in a direction normal to the longitudinalaxis that is sufficient to provide working clearance for the crushingroller 24. Additionally, the external diameter of the reamer body 16 inthis area is reduced or “necked down” as compared to the externaldiameter of the reamer body 16 in the areas adjacent to the lower andupper tapered sockets 40, 46. This necked down configuration of thereamer body 16 provides stress relief in the area of the pockets 18.

The secondary cavity 44 is formed with a flanked trapezium shape whichnarrows at the down hole end of the cavity 44.

The upper tapered socket 46 includes a semi-circular truncated conicalseat of less than or equal to 7° angle to the normal axis of socket 46.As illustrated, this angle is approximately 3°. The upper socket 46 istapered so that the smaller diameter of the socket 46 forms part of thefloor 18 a of the pocket 18. The seat extends for approximately 270° arclength, with the remainder of the arc length opening into the secondarycavity 44. Located substantially centrally of the upper tapered socket46 is a post 52. The post 52 includes a bore 54 which is threaded sothat it can receive the fastener 38. Altematively, as illustrated, athreaded insert 54 a may be located in the bore 54.

FIGS. 5 to 8 illustrate the first retaining means 26. The firstretaining means 26 is formed as a first plug 26 and is arranged to bereceived within the upper tapered socket 46. The first plug 26 is formedas a frustum. The frustum has an angle of less than or equal to 7° toits central longitudinal axis and includes a base 26 a and a top 26 b.As illustrated, the frustum has an angle of approximately 3°. The base26 a is arranged to be positioned lowermost in the lower tapered socket46. The base 26 a has an outer diameter which is smaller than the outerdiameter of the top 26 b. The underside of the base 26 a is shaped toengage with the floor 18 a of the pocket 18 in the area of the uppertapered socket 46. In particular, the base 26 a is shaped so that itwill mate with the post 52.

The first plug 26 includes a fastener-receiving cavity 26 c that opensthrough a sidewall 26 d and also into the base 26 a of the first plug.The cavity 26 c is configured so that the fastener 38 can be positionedwithin and so that the leading end 38 b of the fastener 38 can besecured within the bore 54 formed in the post 52. An aperture 26 e islocated in the top 26 b of the first plug 26 and is configured so thatthe working end of a tool can be passed there through. This enables thefastener 38 to be screwed into and out of the bore 54 of the post 52.

Formed in the top 26 a of the first plug 26 is a pair of bores arrangedto receive the self locking pins 38 a. The self locking pins 38 a areconfigured to properly locate and lock the fastener 38 within thefastener-receiving cavity 26 c.

The sidewall 26 d of the first plug 26 also includes an elongateconnector screw slot 26 f which enables the first plug 26 to beconnected to a connector screw 70 which extends from the enlarged head22 a of the roller pin 22. The connector screw slot 26 f includes athreaded upper portion 26′f which is arranged to receive a threadedretaining plug 72 (FIG. 19). Prior to receiving the retaining plug 72,the threaded upper portion 26′f is sized to enable the head 70 a of theconnector screw 70 to pass there through. In this manner, the head 70 aof the connector screw 70 can be inserted into the connector screw slot26 f and then the shank of the screw 70 can be moved along the length ofthe slot 26 f. The connection between the screw 70 and the first plug 26will be described in more detail subsequently.

As best illustrated in FIG. 3, the fastener 38 is a socket headfastener. The head of the fastener 38 is arranged to be located withinan upper portion of the cavity 26 c so that when the fastener 38 isscrewed into the post 52, the first retaining means 26 is drawn into thelower tapered socket 46 and when the fastener 38 is unscrewed, the firstretaining means 26 is lifted out of the upper tapered socket 46. Theconfiguration of the sidewalls of the lower tapered socket 46 and theshape of the head 22 a of the roller pin 22 facilitate this action ofthe first retaining means 26. As the first retaining means 26 (firstplug 26) is connected to the roller pin 22, movement of the first plug26 in and out of the upper tapered pocket 46 will result in movement ofthe entire roller cartridge 20 in and out of the pocket 18.

FIGS. 9 to 11 illustrate the second retaining means 28. The secondretaining means 28, or second plug, is formed as a frustum. The frustumhas an angle of less than or equal to 7° to its central longitudinalaxis. As illustrated, this angle is approximately 3°. The second plug 28has a base 28 b, a top 28 c and a sidewall 28 d. The base 28 b has alarger external diameter than the top 28 c and is arranged forpositioning lowermost within the upper tapered socket 40. A bore 28 e isformed in a flat portion of the sidewall 28 d of the second plug 28. Thebore 28 e extends substantially perpendicular to the centrallongitudinal axis thereof. The bore 28 e is arranged to receive a secondend 22 b of the roller pin 22. The bore 28 e is sized for a sliding fitwith the second end 22 b of the roller pin 22.

A threaded aperture 28 f is formed in the base 28 b of the second plug28. The threaded aperture 28 f is arranged to receive a retaining screw29 which locates the second end 22 b of the roller pin 22 within thesecond plug 28. The engagement of the retaining screw 29 with the rollerpin 22 will be described in more detail subsequently.

Formed in the sidewall 28 d of the second plug 28 is a minor bore 28 j.The function of the minor bore 28 j will be explained subsequently.

As mentioned previously, the second plug 28 has a lug 28 k formed on thelower part thereof. The lug 28 k is arranged to engage within thesecurity recess 40 b formed in the lower tapered socket 40. Thisengagement serves to better retain the roller assembly 20 within thepocket 18.

FIGS. 12 to 14 illustrate the crushing roller 24. The crushing roller 24is formed as a hollow cylindrical member having a central bore which issized to receive the shank of the roller pin 22. The crushing roller 24has reduced diameter portions at each end for primary engagement of thecrushing roller 24 with the walls of the well bore. A secondaryengagement diameter is formed therebetween and is studded with aplurality of buttons 60 (not shown in FIGS. 12 to 14). The buttons 60are preferably domed shaped tungsten carbide buttons that are eachmounted within an aperture 62. The carbide buttons 60, in accordancewith a preferred embodiment, are arranged in four rows of eight and areset on a left-hand 3.31699″ pitch helix. Each row is separated by 90° ofangular rotation and the starting point for each row commences in aprogressive step equal to 0.125× 1/9^(th) of the helical datum curvelength. Each button 60 is spaced at 1/9^(th) of the helical curvelength.

It will be appreciated by those skilled in the art that the abovearrangement of buttons 60 on the crushing roller 24 provides a veryefficient use of the carbide buttons and thus significantly less carbideis used. This reduction in carbide use is also expected to reduce thetorque loading in the drill string. It will further be appreciated thatother arrangements of the carbide buttons on the crushing roller areenvisaged. Advantageously, the carbide buttons are arranged so thatduring use they provide substantially complete coverage of the portionof the wall of the well or drill hole being reamed. In other words, thecontact area of the various carbide buttons with the portion of thedrill hole being reamed overlaps.

Located between each of helically spaced rows of buttons 60 are flutes64. There are four flutes 64 and they are generated on the same helicaldatum path as the apertures 62. The flutes 64 are arranged to enableincreased mud flow past the crushing roller 24 and to increase theclearance through which the crushing residue from the rotary rollerreamer 10 can pass.

The inclusion of primary engagement diameters at the respective ends 24a, 24 b of the crushing roller 24 enables the rotary roller reamer 10 tobe bi-directional (i.e. either up hole or down hole in its application).Seven holes 62 a are located in each primary diameter for the insertionof further domed tungsten carbide buttons 60 a. The holes 62 a areequally spaced and circumferentially drilled on the surfaces normal tothe roller central axis.

As illustrated in FIG. 12, a further hole 62 b drilled through to thecentral bore is formed in each of the primary engagement diameters. Eachhole 62 b is tapped with a female thread and is arranged to receive apressure plug 63. Each hole 62 b has the dual function of a greaseinjection port and a purge port. The use of the pressure plugs 63 willbe described in more detail subsequently.

As illustrated in FIG. 13, a pair of seal retention grooves 66 is formedwithin the wall of the central bore of the crushing roller 24 and arearranged to receive respective seals 34 a, 34 b. As shown, the seals 34a, 34 b are simple o-rings. However, the use of other types of seals isenvisaged.

Also shown in FIG. 13 are further annular grooves 24 c intermediate theends of the bore of the crushing roller 24. Each groove 24 c is arrangedto receive a stabilizing band 75. As best illustrated in FIG. 21, eachstabilization band 75 is a band which is broken at point A to provide agap between the respective ends 75 a, 75 b of the band. The ends 75 a,75 b terminate at an angle of about 45° (See FIG. 23). Termination atother angles is envisaged.

Each stabilization band 75 is sized to provide a minimal running fitabout the shank of the roller pin 22 and to float within its respectivegroove 24 c. In this embodiment metric fit D9h8 is adopted. Thestabilization band 75 may either be rotatable with the roller pin 22 orwith the crushing roller 24.

Such a stabilizing band 75 is preferably made of a material that isreasonably hard and has a relatively low coefficient of friction. Such amaterial may have a Shore D hardness of about 67, a static coefficientof friction of about 0.09 and a dynamic coefficient of about 0.13. Thismaterial may be a fluoropolymer selected from the range ofpolytetrafluorethylenes (PTFE) marketed by DuPont under the TEFLON®trade mark. However, more preferably, such a material will bestrengthened by the addition of filler, such as with a glass, bronze ornickel filler. Ideally, the material will be a bronze filled PTFE.

In this form, the stabilizing band 75 assists in maintaining therotation of the roller pin 22 substantially stable about itslongitudinal axis and along its entire length. In this respect, in somesituations, a seals 34 a, 34 bmay be somewhat sensitive to end-to-endbounce of the roller pin 22, such as would normally be expected due tothe reasonably severe impact compression encountered by the rollerassembly 20 during operation. The additional use of a stabilizing band75 of this general type will thus assist with the smooth operation ofthe roller assembly 20.

FIGS. 15 to 18 illustrate the roller pin 22. The roller pin 22 includesa central longitudinal bore 22 c (best shown in FIGS. 3 and 15) thatopens through the lower end 22 b. The bore 22 c in the shank of theroller pin 22 forms a lubricant reservoir. A side port 22 d extendsbetween the lubricant reservoir 22 c and a primary lubricantdistribution groove 22 e. The primary lubricant distribution groove 22 eextends longitudinally of the roller pin 22. As best shown in FIGS. 16and 17, the primary lubricant distribution groove 22 e is formed in a“figure 8” configuration.

It will be appreciated that the lubricant reservoir 22 c enables alubricant to be stored in the roller pin 22 and subsequently supplied,via the side port 22 d, to the distribution groove 22 e during rotationof the crushing roller 24 about the roller pin 22. The lubricant isdistributed over the shank of the roller pin 22 as the crushing roller24 rotates thereabout. The seals 34 a, 34 b retain the lubricant on theshank of the roller pin 22.

A second side port 22 i is located adjacent the second end 22 b of theroller pin 22 and intersects with the lubricant reservoir 22 c. The sideport 22 i opens into a groove 22 j. The function of the groove 22 j andthe side port 22 i will be described below.

Also formed adjacent the second end 22 b of the roller pin 22 is atransverse retaining slot 22 g. The retaining slot 22 g is arranged sothat the leading end of the retaining screw 29 in the second retainingmeans 28 can be located in the retaining slot 22 g. In this manner, theroller pin 22 can be oriented relative to the second retaining means 28.The use of a retaining slot 22 g enables limited rotation of the rollerpin 22 after connection to the second plug 28.

As best shown in FIGS. 3 and 20, the pressure equalization means 36 ispositioned against a counter bore formed in the lubricant reservoir 22c. When the roller cartridge 20 is located in the pocket 18, the portionof the lubricant reservoir 22 c to the right side (as shown in FIG. 3)of the pressure equalization means 36 opens into the bore 28 e of thesecond plug 28. The second side port 22 i of the roller pin 22 opensinto the groove 22 j (FIG. 20) which intum aligns with the minor bore 28j formed in the second plug 28. The minor bore 28 j of the second plug28 opens to the area surrounding the crushing roller 24. Thus, it willbe appreciated that there is a pressure flow path from the areasurrounding the crushing roller 24 to pressure equalization means 36.

The pressure equalization means 36 acts to ensure that the pressure ofthe lubricant within the bearing cavity (i.e. the clearance between theroller pin 22 and the crushing roller 24) is substantially equal to thepressure of the drilling mud which completely envelopes the rotaryroller reamer 10 during a reaming operation. It is important to equalizethis pressure so as to prevent the seals 34 a, 34 b from blowing in orout.

The pressure equalization means may take the form of a filter 36. In oneembodiment, the filter 36 may be a sintered metal filter. The sinteredmetal filter may have an alloy composition of 68% copper, 27% nickel and5% tin and a micron capture equal to or about 30 μm. The pressureequalisation means may adopt other configurations.

As best illustrated in FIGS. 3, 18 and 19 the head 22 a of the rollerpin 22 is shaped to mate with the sidewall 26 b of the first plug 26.Thus, the head 22 a is configured as a flanked trapezium shaped solidwith a conical cut in its outer face.

The head 22 a includes a blind bore 22 f which is coincident with theelongate axis of the roller pin 22. The bore 22 f is threaded to enableconnection of the connector pin 70 thereto. This connection will bedescribed in detail subsequently.

The first thrust ring 30 is formed as a solid ring of low friction metalor reinforced polymer which bears against the roller side face of thehead 22 a of the roller pin 22 and the face of the first end 24 a of thecrushing roller 24. The first thrust ring 30 is designed to accept thevertical thrust imparted from the sidewalls of the drill hole on thecrushing roller 24 as a result of the rotating upward travel of therotary roller reamer 10. The first thrust ring 30 is a sacrificialthrust ring.

The first thrust ring 30 has an internal o-ring seal 30 a arranged toprovide a small amount of shock absorption between the inside diameterof the thrust ring 30 and the shank of the roller pin 22. The o-ringseal 30 a also acts as a barrier to the flow of drilling mud.

The second thrust ring 32 is a solid ring of low friction metal orreinforced polymer which bears against the second end 24 b or thecrushing roller 24 and the face of the second plug 28. The second thrustring 32 is designed to accommodate the vertical thrust imparted from thesidewalls of the drill hole on the crushing roller 24 as a result of therotating downward travel of the rotary roller reamer 10 within the holebeing drilled. The second thrust ring 32 is a sacrificial thrust ring.

The second thrust ring 32 has an internal o-ring seal 32 a arranged toprovide a small amount of shock absorption between the inside diameterof the thrust ring 32 and the shank of the roller pin 22. The o-ringseal 32 a also acts as a barrier to the flow of drilling mud. The o-ringseals 32 a, 32 b are preferably made of a fluoroelastomeric compound.

The assembly process for a roller assembly 20 is as follows. A firstthrust ring 30 is slid along the shank of the roller pin 22 until itabuts the head 22 a of the roller pin 22. A crushing roller 24 withseals 34 a, 34 b and stabilization bands 75 in position and carbide tips60 fitted, is then slid onto the shank of the roller pin 22 until thefirst end 24 a of the crushing roller 24 abuts the first thrust ring 30.The filter 36 is then seated against the counter bore of the lubricantreservoir 22 c.

At this stage, grease is injected into the crushing roller 24 via one ofthe holes 62 b (“the first hole 62 b”). The grease is injected untilgrease flows through the hole 62 b (the “second hole 62 b”) in the otherprimary engagement diameter of the crushing roller 24. A pressure plug63 is then installed to seal off the second hole 62 b.

Grease injection is continued until lubricant flows through thelubricant reservoir 22 c and out through the pressure equalizationfilter 36. At this point, the grease injection equipment is removed anda pressure plug 63 is fitted in the first hole 62 b.

The second thrust ring 32 is then positioned on the shank of the rollerpin 22 until it abuts with the second end 24 b of the crushing roller24. Finally, the second plug 28 is slid onto the end of the roller pin22 so that the trailing end of the second thrust ring 32 is locatedflush against the flat portion of the sidewall 28 d of the second plug28. The retaining screw 29 is then located in the threaded aperture 28 fand screwed inwardly so that it locates within the retaining slot 22 gformed in the shank of the roller pin 22.

The fastener 38 is then inserted in the fastener-receiving cavity 26 cof the first plug 26 and held in position by the self locking pins 38 a.

A steel ball 71 is then dropped in the blind bore 22 f. A connectorscrew 70 is then screwed into the bore 22 f until it is firmly setagainst the steel ball 71. This action ensures a constant depth ofengagement of the first plug 26 to the roller pin 22. The head 70 a ofthe connector screw 70 is then passed through the upper portion 26 f ofthe connector screw slot 26 f in the first plug 26.

Connection between the first plug 26 and the roller pin 22 is maintainedby inserting a retaining plug 72 in the threaded upper portion 26 f ofthe connector screw slot 26 f. The retaining plug 72 prevents the head70 a of the connector screw 70 from inadvertently withdrawing from theconnector screw slot 72.

The positioning of the connector screw 70 in the connector screw slot 26f of the first plug 26 is best illustrated in FIG. 18. The insertion ofthe retaining plug 72 in the threaded upper portion 26 f of theconnector screw slot 26 f is best illustrated in FIG. 19.

As will be apparent, the connection between the head 22 a of the rollerpin 22 and the first plug 26 is such as to allow limited articulation ofthe first plug 26 relative to the roller pin 22, whilst still ensuringproper alignment of the plug 26 relative to the roller pin 22 when theroller cartridge 20 is fitted into a pocket 18 of the rotary rollerreamer 10.

Once the components of the roller assembly 20 have been assembled, theroller cartridge, as it is then known forms a single cartridge which isready for insertion into a pocket 18 of the rotary reamer 10.

A roller cartridge 20 is fitted within a pocket 18 of the rotary rollerreamer 10 as follows. Firstly, the roller cartridge 20 is heldhorizontally so that the second plug 28 is located in a forward positionfacing the end of the lower tapered socket 40. The roller cartridge 20is then tilted towards the floor 18 a of the pocket 18. It is thenlowered into the pocket 18 until the second plug 28 contacts the floor18 a of the pocket 18. The roller cartridge 20 is then slid forward anddown into the pocket 18 until the second plug 28 is seated in the lowertapered socket 40.

During positioning of the second plug 28 in the lower tapered socket 40,the first plug 26 aligns itself relative to the roller pin 22 and theupper tapered socket 46 so that it is properly positioned within thepocket 18 ready to be fastened in position by the fastener 38. This“self aligning” characteristic of the first plug 26 is a consequence ofthe nature of the connection between the first plug 26, the connectorscrew 70, the steel ball 71 and the head 22 a of the roller pin 22.

A hex driver is then inserted through the aperture 26 d in the firstplug 26 and the fastener 38 is screwed into the threaded bore 54 of thepost 52 formed in the floor 18 a of the pocket 18. As the fastener 38 isscrewed into the bore 54 the first plug 26 is drawn into the uppertapered socket 46. FIG. 20 illustrates a roller cartridge 20 beingfitted into a pocket 18 of a rotary roller reamer 10.

It will be appreciated by those skilled in the art that differentnumbers of pockets 18 may be provided on the reamer body 16.Additionally, although the pockets 18 are described as being equallyspaced about the periphery of the reamer body, this need not always bethe case. They may for example be spaced by an exponential orlogarithmic value.

It will also be appreciated that the crushing roller 24 may includedifferent arrangements and numbers of primary engagement diameters (i.e.may adopt a multi step form), carbide buttons; flutes and helixes.

Shown in FIG. 24 is another form of roller assembly 100. The rollerassembly 100 generally includes a roller pin 120 and a crushing roller140. The crushing roller 140 includes a body having a bore formedtherein that is sized to snugly receive therein the shank of the rollerpin 120.

At each end of the bore there is an annular groove in which a seal 220is arranged to be located. It will be appreciated by those skilled inthe art that the seals 220 may adopt different forms and that theannular grooves may be located adjacent to the end of the bore of theroller pin 120.

Also shown in FIG. 24 are further annular grooves intermediate the endsof the bore of the roller pin 120. Mounted within each of the annulargrooves is a stabilising band 260. The stabilising bands 260 areidentical to the stabilising bands 75 shown and described previously inrelation to FIG. 3.

Although the roller assemblies described previously include a fixedroller pin (i.e. non-rotating) and a crushing roller that rotatesthereabout, it will be appreciated that the stabilising bands of thepresent invention may be incorporated in arrangements wherein the rollerpin is not fixed.

It should be appreciated that stabilizing bands in accordance with thepresent invention may find application in many different forms of rollerassemblies. Accordingly, reference to the term “roller assembly” shouldnot necessarily be restricted to roller assemblies of the type used inrotary roller reamers.

It should be noted that these embodiments have been described by way ofexample only, and modifications within the spirit and scope of thepresent invention are envisaged.

1-15. (canceled)
 16. A stabilizing band for a roller assembly, theroller assembly having a roller pin mounted within a bore of a roller,the stabilizing band being configured so as to fit tightly about theroller pin with a minimal running fit and within an annular grooveformed in a wall of the bore of the roller, said stabilizing band beingbroken so as to provide a gap between respective first and second endsof the stabilizing band.
 17. A stabilizing band according to claim 16wherein the first and second ends each terminate at an angle of about45°.
 18. A stabilizing band according to claim 16 wherein the gapextends for approximately 15° of arc of the stabilizing band.
 19. Astabilizing band according to claim 16 wherein it is configured to floatwithin the annular groove so that it may either be rotatable with theroller pin or with the roller.
 20. A stabilizing band according to claim16 made of a material that is reasonably hard and has a relatively lowcoefficient of friction.
 21. A stabilizing band according to claim 20wherein the material has a Shore D hardness of about
 67. 22. Astabilizing band according to claim 20 wherein the material has a staticcoefficient of friction of about 0.09.
 23. A stabilizing band accordingto claim 20 wherein the material has dynamic coefficient of friction ofabout 0.13.
 24. A stabilizing band according to claim 16 made from afluoropolymer material.
 25. A stabilizing band according to claim 24wherein the fluoropolymer material includes a filler.
 26. A stabilizingband according to claim 25 wherein the filler is a glass, bronze ornickel filler.
 27. A stabilizing band according to claim 16 made from abronze filled PTFE.
 28. A roller assembly including a roller pin, aroller, at least one seal and at least one stabilizing band configuredto fit tightly about the roller pin with a minimal running fit andwithin an annular groove formed in a wall of a bore of the roller, saidstabilizing band being broken so as to provide a gap between respectivefirst and second ends of the stabilizing band.
 29. A roller assemblyaccording to claim 28 wherein the roller pin is fixed and the roller isarranged to rotate thereabout.
 30. A roller assembly according to claim28 including two seals and two stabilizing bands.